Recent trends in the electronics industry have been toward increased integration in the form of multi-chip modules and software-controlled power management. Conventional thermal management techniques rely on spreading the heat generated in the active areas of the device and ultimately rejecting it to the environment via a heat sink. The shortcoming of this spreading technique is apparent with multi-chip modules: while temperatures of the active areas are reduced, the spreading causes inactive areas of the device to heat up along with severe temperature gradients. Ideally, the device should maintain a uniform temperature, independent of local activity. Reducing temperature gradients by locally cooling active or heating inactive areas in the device to a uniform temperature would reduce stresses and increase reliability.
New developments in VLSI integration have lead to a family of Field Programmable Gate Array (FPGA) chips with thousands of high-speed configurable switches (cells) that are capable of unlimited programmability. The setting of each switch is controlled by bits of high-speed RAM spread throughout the chip that has a toggle rate on the order of 220 MHz. By linking the FPGA with an external microprocessor or controller, functions may be implemented that are normally placed on an ASIC. The distinct advantage that FPGAs have over ASICs, is that FPGAs may be quickly reprogrammed. This programmability may be further exploited by coupling the FPGA with a genetic algorithm allowing circuit functionality to "evolve" directly on the FPGA in real time without having to rely on idealized computer simulations of the desired circuit. This approach to circuit design results in efficient electronic circuits that exploit the natural properties of silicon. However, evolved circuits on FPGAs perform satisfactorily only within .+-.5.degree. C. of the temperature at which the circuit evolution took place. As the temperature increases or decreases beyond this range, the circuit performance significantly degrades. Hence, there is a clear problem with evolutionary hardware: how to evolve a circuit from processes that generate unequal heat and thus vary with temperature, such that the circuit can perform adequately over a wider range of temperatures.
Similar thermal management problems arise for sensors and other temperature-sensitive devices that must maintain precise temperatures in the presence of changing external fields and environments. These devices include: infrared detectors, gyros and accelerometers, photoresistors for IR spectroscopy, CCD devices, and laser and light-emitting diodes. Thus, there is a need in the art for maintaining uniform temperatures on electronic devices in the presence of changing internal or external temperature fields.